Source

File: wp-includes/sitemaps/class-wp-sitemaps.php

public function init() {
		// These will all fire on the init hook.
		$this->register_rewrites();

		add_action( 'template_redirect', array( $this, 'render_sitemaps' ) );

		if ( ! $this->sitemaps_enabled() ) {
			return;
		}

		$this->register_sitemaps();

		// Add additional action callbacks.
		add_filter( 'pre_handle_404', array( $this, 'redirect_sitemapxml' ), 10, 2 );
		add_filter( 'robots_txt', array( $this, 'add_robots' ), 0, 2 );
	}